日本落叶松早期选择中未来净值模型的应用

为加速日本落叶松的遗传改良进程，缩短育种周期，建立了用于早期选择的未来净值模型。结果表明，不同轮伐龄、利率和其他经济学因子对利用最大未来净值模型确定最佳早期选择年龄有较大的影响，对日本落叶松早期选择的有效性，基本参数对未来净值模型的影响以及最佳选择年龄的收敛问题也进行了探讨。     

晋中盆地不同土地利用类型的植物多样性

区域土地开发利用明显影响植物多样性,因此探讨和分析其影响机理和规律显得非常重要。本文以晋中盆地为研究对象,选取林地、内陆滩涂、果园、墓地、田坎及公路用地共6种土地利用类型(简称地类)随机抽取样地,然后在样地上设置调查样方,采用Jaccard相似性指数、Gleason丰富度指数对调查数据进行处理,分析了地类对植物多样性的影响。结果表明:墓地与田坎的群落植物物种组成相似性最高,Jaccard相似性指数值为0.552;果园与公路群落植物物种组成相似性最低,Jaccard相似性指数为0.216;各种地类上植物的Gleason丰富度指数算术平均值大小依次为墓地田坎内陆滩涂林地果园公路用地;t-检验结果显示,林地与内陆滩涂、林地与果园、林地与墓地、内陆滩涂与果园、墓地与田坎之间的植物物种丰富度差异未达到显著水平,而其他地类两两之间的差异均达到了显著水平。人为干扰强度不同是造成不同地类植物多样性差异的主要原因,研究结果为今后合理利用土地、采取有效措施保护生物多样性提供了参考依据。     

Effects of air temperature, photoperiod and leaf age on foliar senescence of western larch (Larix occidentalis Nutt.) in environmentally controlled chambers

We induced foliar senescence in western larch (Larix occidentalis Nutt.) needles (100 to 400 d old) in chambers set to combinations of photoperiod (8 or 16 h) and air temperature (8 or 15°C). We used regression analysis to estimate the effects of air temperature, photoperiod, provenance and leaf age on the date of decline in chlorophyll, photosynthesis, and chlorophyll a/b ratio. Increased air temperature delayed the decline in chlorophyll and photosynthesis without affecting chlorophyll a/b: seedlings with 200-d-old needles placed under 8h days and 8°C lost chlorophyll, photosynthesis and chlorophyll a/b in 22, 37 and 63d, respectively, while those senescing under 15°C lost them in 54, 61 and 63d. Extended photoperiod delayed the decline in chlorophyll but not photosynthesis or chlorophyll a/b ratio: the 200-d-old needles placed in 8°C and 16 h photoperiod lost chlorophyll, photosynthesis, and chlorophyll a/b in 34, 37 and 63 d, compared with 22, 37 and 63 d for seedlings in 8 h days. Our analysis shows that it is possible to quantify the extent to which the timing and process of senescence vary with environmental conditions.     

Role of root systems of eastern larch and white spruce in response to flooding

Abstract. Soil flooding causes rapid reductions in transpiration, stomatal conductance and photosynthesis of many woody plants, which can decrease growth and ultimately result in plant death. This study was conducted to determine the role of the root system in the flooding response. Eastern larch ( Larix laricina ) seedlings were grown in Plexiglas tubes in which water uptake by flooded and unflooded roots was measured independently. Further flooding studies were conducted with eastern larch and white spruce ( Picea glauca ) in which stems were girdled. Root hydraulic properties were analysed using pressure-flow relationships. Transpiration rates of partially flooded plants declined more slowly than fully-flooded plants. Water uptake by unflooded roots of partially flooded seedlings increased momentarily with flooding. After lOd, flooding caused little change in root hydraulic conductance, a decrease in root system reflection coefficient, and an increase in osmotic permeability. Stem girdling had little effect on stomatal conductance and transpiration in comparison to flooding effects. The response of plant tops to flooding appears to be xylem-mediated and in proportion to the amount of root system flooded. Root hydraulic conductance appears to be unaffected by flooding except for a possible temporary increase on the first day following flooding treatments.